Materials Research: Hydraulic curing of ZP-150 powder

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ezrec
Posts: 112
Joined: Sat Aug 15, 2015 1:31 pm

Materials Research: Hydraulic curing of ZP-150 powder

Post by ezrec »

The ZP-150 powder (which is a talc-fine cement powder + sugar) has a very interesting property that I have been exploiting.

After accidentally dropping a part into a bucket of water, an hour later I found that the part, although slumped and bent, was now rock hard, and very durable, paintable, and water resistant.

After some experimentation, I have developed the following technique for hydraulic curing of ZP-150 parts as a cheap and effective alternative to epoxy and cyanoacrylate infiltration:
  • Select a container slightly larger than your part
  • Get a quantity of very fine sand - must be absolutely dry and free flowing
  • Put 1cm of dry sand on the bottom of the container (only needed if your part doesn't have a flat base)
  • Place part on sand
  • Fill container with sand, ensuring that sand is touching all exposed part surfaces
  • Gently tap container until sand is packed
  • Slowly (important!) fill container with water, allowing air to escape though a dry patch in the sand
    * DO NOT MOVE OR VIBRATE CONTAINER DURING THIS PROCESS
  • Leave aside for 30 minute to 2 hours
    * DO NOT MOVE OR VIBRATE CONTAINER DURING THIS PROCESS
  • Invert container, and wash off sand
At this point, the part will be much stronger, but will still be slightly brittle, and have a rough sandy surface
  • Place part in a container of fresh waster + vinegar (diluted acetic acid) of a 900ml:10ml ratio.
  • Let sit for a few hours or overnight
    * This will further strengthen the part, and loosen the weak bond to the sand
  • Rise off surface sand with fresh water
  • Let dry in a 90C oven until completely dried
Done! Part should now have a 'ceramic' like feel to it, and will be water resistant and paintable.

See video of durability test here:

http://youtu.be/g78YgEdzeeE
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dragonator
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Re: Materials Research: Hydraulic curing of ZP-150 powder

Post by dragonator »

That is just shocking how strong that is. I comes close to CA treated parts, and your way is without any nasty chemicals. It does seem a bit laborious, but considering the nastiness of CA, I think this is a worthy processing technique.

Would it be possible to just coat the surface with a tiny amount of water, by using something like a spray bottle with water. It might not give strength throughout the part, but it might make the surface a stronger without a ton of post processing.
ezrec
Posts: 112
Joined: Sat Aug 15, 2015 1:31 pm

Re: Materials Research: Hydraulic curing of ZP-150 powder

Post by ezrec »

I've tried the water spray method (10:7 ratio of water to Epson salts by volume, as per ZCorp recommendation), but the problems I had were:
  • Initial spraying of the salt water caused slumping of fine details
  • The salt water mix only hardened the outer surface (about 1mm penetration)
  • Over drying is still required for this process (2 hours or so at 90C)
  • After about 2 to 3 days in a humid environment, the hardness decreased, to the point where it was no stronger than an untreated oven dried part.
The biggest advantage, other than hardness, is that the hydraulically treated parts - using sand to preserve form and detail - is that once cured, the part is porous, yet will not dissolve or slump in water.

This allows secondary infiltration with a wider variety of materials (aqueous glues or colored inks, for example) than untreated parts.

The only really laborious part is drying the sand in an over after processing to reclaim it. Everything else is a "5 minutes of doing something, 2 hours of waiting" step.
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